The present disclosure relates generally to the field of signal processing. More particularly, the present disclosure relates to methods of and systems for decoding signals.
Signal processing is utilized in communication (e.g., radio, cell phone, etc.) and sensing applications (e.g., radars, imaging, etc.), as well as other applications. According to one particular application, signal processing is used in sensing and communications applications to obtain data that has been modulated on a radio frequency (RF) or optical signal.
Decoders are often provided in the signal processing path to detect symbols representative of data modulated on input signals. Decoders can be utilized in a variety of RF systems, including time division multiple access (“TDMA”) systems, code division multiple access (“CDMA”) systems, orthogonal frequency division multiple access (“OFDM”) systems, etc. One example of a decoder is a maximum likelihood sequence estimator (MLSE) (e.g., a Viterbi decoder)
A Viterbi decoder is often utilized with continuous signals, such as signals using continuous phase modulation (CPM). There are many CPM signaling schemes including minimum shift key (MSK) modulation, continuous-phase frequency shift key (CPFSK) modulation, etc. Generally, a Viterbi decoder compares a demodulated signal in a base band frequency represented as a series of symbols with a set of reference symbols to determine which symbols have been transmitted.
RF signals, as well as other signals, can encounter impairments which can affect the ability of the decoder to determine the identity of the received symbol. In one example, symbol interference (e.g., intersymbol interference (ISI)) can perturb the received symbol when an RF signal is propagated through space. Accordingly, in conventional receiver architectures, the set of known reference patterns for all possible received symbols does not necessarily contain an exact match for an ISI corrupted received symbol.
Inter symbol interference and other impairments can be caused by satellite transponders or reflections off of surfaces such as aircraft or the like. Reference symbol patterns have been adjusted in accordance with an average phase error measured in the laboratory to accommodate changes in the received symbol pattern. However, this technique cannot adjust to errors that are not consistent or are not known in the laboratory.
Accordingly, there is a need for a system and method that improves symbol decoding. Further still, there is a need for a system and method of decoding that is adaptive. Yet further still, there is a need for a receiver that provides adaptive equalization for band limited continuous phase modulation. Yet further, there is a need for a decoder that adaptively compensates for intersymbol interference (ISI), such as ISI caused by channel filtering. Still further, there is a need for a system and for or a method of decoding symbols using reference symbols that are continually adjusted in accordance with real world errors.
Other features and advantages will be made apparent from the present specification. The teachings disclosed extend to those embodiments which fall within the scope of the appended claims, regardless of whether they accomplish one or more of the aforementioned needs.